Temperature effects on the forces, moments and moment to force ratio of nickel-titanium and TMA symmetrical T-loops.
OBJECTIVE
To test the null hypothesis that temperature has no effect on the force, moment, and moment to force ratio (M:F) of nickel-titanium (NiTi) and titanium molybdenum alloy (TMA) T-loops.


METHODS
Twelve symmetrical T-loops were constructed from NiTi and TMA rectangular wires (N = 24). For each material, four specimens had 30 degrees preactivation bent into the legs, four had 15 degrees , and the remainder no preactivation. The specimens were mounted on a custom stand incorporating a force and a moment transducer housed in an insulated oven in which the temperature was varied from 10 degrees C to 50 degrees C in 10 degrees increments (+/-0.5 degrees C). The loops were opened in 1-mm increments to a maximum of 8 mm and allowed to return to the rest position. Forces and moments were recorded at each interval; from this, the M:F was calculated. Mixed-model statistical analysis was used to detect differences between mean results of material type, preactivation, and temperature.


RESULTS
Temperature significantly influenced the forces and moments (P < .000) produced by NiTi closing loops, with values increasing as the temperature increased. The M:F ratios of NiTi loops were less affected, with no significant changes with temperature for the 15 degrees and 30 degrees preactivation loops, although some change was noted for the non-preactivated loops. TMA wires showed significance for some force measurements, but were generally not influenced by temperature.


CONCLUSIONS
The hypothesis is rejected. Temperature significantly affected the forces and moments produced by NiTi T-loops, though these changes generally do not affect the overall M:F ratio.
Lim
Yeen
Y
Department of Oral Sciences, University of Otago, Dunedin, Otago, New Zealand.
Quick
Andrew
A
Swain
Michael
M
Herbison
Peter
P
D000497:Alloys / Q000737:chemistry*; D003722:Dental Alloys / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry*; D019415:Torque; D014159:Transducers
D000497:Alloys; D003722:Dental Alloys; C525450:titanium molybdenum alloy; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium